As it is well known, portable image acquisition devices, such as cameras or cell-phones provided with photographic equipment, are equipped with image acquisition sensors 1 being placed in a housing 2 provided with a housing cavity 3 and fixed to the housing 2 by interposition of an adhesive layer 1a, as shown in FIG. 1.
After electrically connecting by means of electrical wires 3a the sensor 1 and the housing 2, for example through wire bonding as shown in FIG. 2, the housing cavity 3 is then closed by a sealing lid 4 by interposition of an adhesive layer 4a. The lid 4 is for example glass made as shown in FIG. 3.
An optical group 5 is then fixed on the housing 2. Generally, the optical group 5 comprises a lens holder 6 and a lens barrel 7 wherein a lens 8 is placed and fixed to the holder 6, as shown in FIG. 4.
In particular, during a focusing step of the lens 8 with respect to the sensor 1, the holder 6 is integrally fixed to the housing 2 and the barrel 7 is shifted with respect to the holder 6 in order to find the right optical group 5 focusing point, as shown in FIG. 5.
Particularly, the barrel 7 can be rotated, horizontally and/or vertically shifted until the best focusing point position of the lens 8 is reached with respect to the sensor 1.
The right focusing point being found, the barrel 7 must be locked to the holder 6.
A first known technical solution to lock the barrel 7 to the holder 6 is shown in FIG. 6.
According to this solution, an adhesive layer 9 is interposed between the barrel 7 and the holder 6. In order to allow a stable fixing, mutually cooperating barrel 7 and holder 6 portions, during the fixing step, are provided with grooves 10 allowing the adhesive layer 9 to be better supported.
Although advantageous under many aspects, this first solution has several drawbacks.
Particularly, this kind of solution is essentially based on manual production, since it is difficult to control the dispensing of this adhesive layer 9 between the barrel 7 and the holder 6 in automatic production tools.
Moreover, as it is difficult to distribute uniformly the adhesive layer 9 between the barrel 7 and the holder 6, the lens 8 can easily lose the alignment with the sensor 1, since it has been verified that the barrel 7 is attracted in the direction where there is a higher quantity of adhesive layer.
A second solution to lock the barrel 7 to the holder 6 provides instead the use of a metallic undulated ring or made of materials being different from the ones forming the barrel 7 and the holder 6, which is interposed between the barrel 7 and the holder 6. The pressure exerted by the ring tends to keep the barrel 7 in position with respect to the holder 6.
Although responding to the aim, also this solution has some drawbacks.
In fact after focusing it is difficult for the ring to ensure that the relative position is kept between the barrel 7 and the holder 6.
Therefore the image acquisition devices manufactured with these known techniques are affected by repetitiveness problems, limiting the application thereof at industrial level, and increasing the production costs thereof. Particularly, shifting the lens focusing axis and/or point by a few microns with respect to the sensor, the image detected by the sensor itself is no longer uniform. Particularly, an image portion detected in correspondence with the lens edges is of considerably different quality than an image portion detected in correspondence with the lens center.